logstash/logstash — pull request #922 by dploeger (2014-01-09 15:56:44+00:00)
Title: Multiline: Support for only merging a specific regexp group

Multiline now supports a "onlygroup" parameter, which replaces the message of subsequent events with only the regexp group specified in the pattern-parameter.

For example:

GARBAGE First line
GARBAGE Second line

Configuration:
```
filter {
multiline {
pattern => "GARBAGE (?.*)",
what => previous,
onlygroup => "realmessage"
}
```

Result:

event["message"] => "GARBAGE First line\n Second line"